Gretch

Well Andy, the first streak of luck you mention above, you DID have something to do with..................

If you worked as hard at fubar'ing your LH as you did at running women off with their hair on fire, you must have been pissing on those two LHs every night after your commute!



Just teasing Bro......... hope you get it sorted out. Don't discount that something in your car is causing the LHs to go bad. It happened once to me with coils and I went through 3 of them before I got it sorted!

Mongo

One thing I did check right after I broke down was to see if my relays were hot on the LH and fuel pump. They were not. NOt sure if relays would be an idea there to check. They seem to be functioning properly. I am probably going to buy 2 new ones as cheap insurance.

bd0nalds0n

What factors would cause an unpowered electrical component to fail, just sitting there?

Courtshark

#1 would be moisture/condensation.

#2 would be squirrels.

Mongo

It certainly isn't spiders... Although, those things are all over my fiancee's Jetta. I was driving it last night to get some groceries and one just bungie jumped outta the damned visor while I was doing 55 on the road. Smashed it against the horn pad. If you see a guy driving a jetta and honking, that's probably me smashing another one.



On a side note, I have 4 hours of my morning dedicated tomorrow to inspecting wiring on this car.

John Speake

Open circuit inputs = high impedance, maybe some kind of static event ?(atmospheric)

Who knows, it's all voodoo :-)

Mrmerlin

I would take both of your LHs and swap them into a good running car and see what happens.
No need to possibly damage another one

Mongo

I do know it was running really good with this LH before it crapped out. Most likely, that was the way it should be running

danglerb

Would a short in the injector wiring potentially blow an LH?

I don't know if it applies to the LH, but electrolytic capacitors frequently go bad over time, often failing a short time after an old working spare is put into service.

John Speake

No, I've not seen a blown up imjector output stage in an LH yet.

I change the main electroytics as a matter of course during a rebuild, although again I've never found one faulty.

Rich9928p

I see and rebuild a steady stream of failing 1987 and newer Porsche 928 LHs (Not so many 1985 - 86s because they don't use the hybrid circuit). The hybrid circuit is the main cause of LH failure (other items fail, but hybrid circuit failure is the major item). The ONLY cause of clicking fuel injectors when the ignition turned on but not cranking is a failed LH, and it is specifically caused by one of the circuits on the hybrid chip. Running excessively rich is caused by the failure of another hybrid circuit. If you are lucky, the LH just dies. Why? Because diagnostics are a lot easier if the engine won't start rather than if it slowly fails or does a bunch of intermittent strange things.

One of my customers purchased a used LH, it lasted six months. He purchased a second used one, that one lasted another few months. He finally decided to go with a rebuilt one and hasn't had a problem since.

Another customer spent over $1500 on mechanic diaganostic fees before the determination it was the LH failing, sadly his shop wasn't familiar with the foibles of LH failure. If they did know how they fail, he could have saved a good amount of cash.

IMHO the failure cause is a passivation failure of the custom ICs on that hybrid chip (see the photo, the circuits under the clear silicon blob) - in layman's terms they are rusting to death. This is the reason why LHs can die while sitting on the shelf. Most electronic components have a greater failure rate while under operation - but not if the passivation fails. So no acts of voodo, fear of trickle chargers, or sacrifices of small mammals will save your LH if H2O decides to munch on it.

That is the fact of 1987 and newer Porsche 928 ownership. PS: Volvo and Saab owners have the SAME problems, it is a generic Bosch LH 2.2 and 2.3 generation issue.

Rich9928p

Here is a photo of the hybrid chip - for some reason it didn't post in the previous message.

Mongo

I wonder what they were thinking when they did these chips? Thanks for the explanation Rich. That by far was the best one that helps me comprehend the debacle of 2 birds 1 stone. Right now the car is one expensive paperweight.

Lizard928

Andy, you should have just taken Roger up on his offer...............

Rich, why not post a picture of the updated part that you use?

Rich9928p

What was Bosch thinking?

a) easier manufacturing, major cost reduction, probably higher profit margins for Bosch. They removed a boatload of parts off the board by using this device (compare the 1985 - 1986 25 pin LH with the 1987 and newer).

b) higher reliability (fewer parts can improve reliability). Back in its day, this was pretty advanced electronics.

c) These LHs certainly have lasted longer then their warranty, they're going on 20+ years of age (probably didn't start failing until they were at least 5 years old). Major semiconductor companies spend millions of dollars learning how to passivate chips yet so they can use inexpenive plastic packaging (that also does admit water vapor). Bosch probably had a lot less experience back then and this issue didn't show up until long past their expected life cycle anyway.

There are many newer cars that have ECUs failing at rates like these LHs, and the replacements cost thousands of dollars!